As the techniques used for a network, such as the Internet, have been developed, a business form by which trading and operations are performed through messages communicated via a network has become popular. For this form, the provision of security is very important.
An XML digital signature technique has gradually been established as a data exchange format for use for business communications transmitted across a network, and it is anticipated that the authentication of negotiable instruments and secured transactions can also be effected by applying the XML digital signature technique. A digital signature technique is a technique by which signature information (as digital information) is added to and used for authenticating a digital document. Generally, to provide a signature in such a case, public key cryptography is used. In this case, a signatory prepares signed text by using hashing to prepare a hash of a compressed document and a secret key that only the signer knows, and transmits the original document with the hash. A verifier (a recipient) employs the public key of the signatory and the original document to determine whether the signature is authentic.
The digital signature technique also includes a function for preventing a third party or a recipient (a verifier) from counterfeiting or forging a signature, and a function for preventing a signatory from disavowing his or her signature.
Thus, when a variety of messages are signed using a unique ID number, a function can be implemented for proving that:                1. a message was prepared by a sender,        2. a message was not altered,        3. the same message was not erroneously received twice, and/or        4. a message was transmitted by a sender.        
However, to sign and verify a message using a conventional cryptography library, an application program that employs the digital signature technique must be changed, and this can be quite expensive.
In some cases, a digital signature condition may be established to increase the probative force of a digital signature. As an example, for one digital signature technique, a time limit may be set according to which a signature can be provided only within a predetermined time period, or for another digital signature technique, a condition may be established according to which a signature can not be provided unless a specific process is performed. In these cases, when a specific digital signature is provided as a replacement for an original digital signature, and later, the original digital signature is provided as a post signature, it is convenient for the performance of the operation procedures.
At the same time as a digital signature is provided and verified, the signed message must be stored in a safe log in order to enable the following monitoring. While the stored message can not be altered because it is accompanied by the signature, the message can be browsed. However, since confidential information may be included in a business message, access control is required for a log.